@mixin placeholder($selector) {
    #{$selector}::-webkit-input-placeholder {
        @content;
    }

    #{$selector}:-moz-placeholder { /* Firefox 18- */
        @content;
    }

    #{$selector}::-moz-placeholder {  /* Firefox 19+ */
        @content;
    }

    #{$selector}:-ms-input-placeholder {
        @content;
    }
}